This invention relates to fluid-gauging systems and methods.
Aircraft fuel tanks usually have several probes disposed to measure the height of fuel within the tank at different locations. A Boeing 777 inner wing tank, for example, has eight probes used in fuel height measurement. Probes may be of any conventional kind, such as capacitive or ultrasonic probes. The probes are preferably located in a non-linear fashion, that is so that the locations of no three probes lie on a straight line. In this way, the maximum information can be obtained about the orientation of the surface plane of the fuel. In practice, however, it is not usually possible to locate all probes within a tank so that no three are arranged in a straight line or an almost straight line (that is, with none co-linear) because of limited availability of fixing points, intrusions into the tank and other factors.
The construction of fuel-gauging probes can make them prone to false readings if, for example, there is a blockage of fuel flow into or out of the probe, an accumulation of foam within the probe, adverse thermal stratification conditions, water contamination, damage to the probe or the like. Because the fuel surface may be moving within the tank at some times and be stationary at other times, it is not always immediately apparent when a probe is providing a false height reading.
GB 2352523 describes an aircraft ultrasonic fuel-gauging system having a number of gauging probes in a tank arranged so as to include at least one set of three co-linear probes. The outputs of the probes are supplied to a unit that checks the operation of the probes in co-linear sets by extrapolating height at one of the probes from the outputs of the other probes. Where there are at least two sets of co-linear probes having a common probe it is possible uniquely to identify if that common probe is faulty. The system rejects any faulty probe and uses only the outputs of other probes in computations of fuel quantity. Although this system can function well it may not be suitable for tanks having only a small number of groups of three co-linear probes.
It is an object of the present invention to provide an alternative fluid-gauging system and method.
According to one aspect of the present invention there is provided a system for gauging the quantity of liquid in a vehicle tank including at least three probes arranged to measure the height of liquid at a plurality of different locations within the tank, sensor means for providing an output representative of the attitude of the liquid surface with respect to the tank, and means for comparing the output of a group of at least two of said probes with the attitude derived from the sensor means to determine whether the probe outputs are compatible with the sensed liquid attitude.
The system is preferably arranged to provide an output of liquid quantity derived from only those probes having outputs compatible with the sensed liquid attitude. The sensor means may include inertia sensing means. The probes are preferably acoustic gauging probes. The liquid may be fuel and the vehicle may be an aircraft.
According to another aspect of the present invention there is provided a method of fluid-gauging including the steps of receiving outputs from a set of at least two probes, providing an indication of the height of fluid at each of said probes, receiving an output representative of the attitude of the fluid surface with respect to the probes, and using the attitude output to determine whether the indication of fluid height provided by any of the probes is incompatible with the height provided by any others of the probes.
The method preferably includes the step of providing an output indicative of fluid quantity derived from only those probes having outputs compatible with the sensed fluid attitude. The output representative of attitude is preferably derived inertially.
According to a further aspect of the present invention there is provided a system for performing a method according to the above other aspect of the invention.
An aircraft fuel-gauging system and method according to the present invention, will now be described, by way of example, with reference to the accompanying drawing.